A detection device has been proposed that detects a foreign object, such as a tiny piece of tape, attached on a surface of a sheet-like detection target such as banknotes or securities by detecting capacitance between electrodes caused by the detection target (see Patent Literature 1). A device for determining whether a detection target is authentic is also proposed that includes a capacitance sensor for detecting a change in capacitance and a sensor for detecting other information (see Patent Literature 2). The capacitance sensor that is a device for detecting the change in capacitance as disclosed in Patent Literatures 1 and 2 detects the change in capacitance between electrodes caused by the detection target passing between the electrodes of a parallel-plate capacitor.
The devices disclosed in Patent Literatures 1 and 2 are intended to be applied to an apparatus necessary for determination on authentication of the sheet-like detection target such as banknotes or securities. Examples of such an authentication determination apparatus include an automated teller/telling machine (ATM), a money changer, a cash dispenser, a ticket machine, a vending machine, and the like. To determine whether the detection target is authentic, some ATMs include a paper thickness detection device that includes a roller and an ultrasonic sensor and detects a thickness of paper. Use of the paper thickness detection device enables determination of banknotes and securities having an unusual thickness of paper. Attachment of foreign objects on the banknotes and securities can be detected based on the determination of the paper thickness, the change in capacitance, and the like.
For reuse, damaged banknotes and securities may be repaired with, for example, a transparent resin tape. To prevent circulation of the repaired banknotes and securities on the market, the ATM detects the attachment of foreign objects on the banknotes and securities that are the detection target, and collects the detected banknotes and securities inside the ATM. As disclosed in Patent Literature 2, for example, the ATM detects banknotes and securities repaired with a tape, paper, or the like. When such a detected banknote is a banknote with just a tear repaired, the banknote is collected into a reject box, whereas when the detected banknote is an altered banknote made by connecting strip-like pieces of banknote together, the banknote is returned to a banknote depositing and dispensing port. A banknote thickness sensor disclosed in Patent Literature 2 detects that the transferred detection target is at least double-stacked.